Will the Apple Watch Series 9 GPS cellular bought in the USA work in Israel?

no, people report the apple watch type sold in usa, canada, mexico and Porto rico use a different eSim system than the rest of the world so if you buy one it will just work as a normal non cellular gps version

The warranty is not international, as warranties are country specific because of different laws in different countries on warranties. You will either have to pay for any repairs out-of-pocket, or return the the U.S. for warranty repairs.

While I do not think it will be a problem, some countries impose feature restrictions. You should cross check to make sure.

https://www.apple.com/watchos/feature-availability

In theory, the Series 9 is the same model in the U.S. and Israel, however, the volunteers here do not have much experience on the Series 9 being used in countries where it was not purchased, so we are guessing.

Feel free to let us know if it works.